Crosstime Traffic Series by Harry Turtledove

Jeremy Solter is a teenager growing up in the late 21st century. During the school year, his family lives in Southern California-but during the summer the whole family lives and works in the city of Polisso, on the frontier of the Roman Empire. Not the Roman Empire that fell centuries ago, but a Roman Empire that never fell.For we now have the technology to move between timelines, and to exploit the untapped resources of those timelines that are hospitable to human life... moreJeremy Solter is a teenager growing up in the late 21st century. During the school year, his family lives in Southern California-but during the summer the whole family lives and works in the city of Polisso, on the frontier of the Roman Empire. Not the Roman Empire that fell centuries ago, but a Roman Empire that never fell.For we now have the technology to move between timelines, and to exploit the untapped resources of those timelines that are hospitable to human life. So we send traders and businesspeople-but as whole-family groups, in order to keep the secret of Crosstime Traffic to ourselves.But when Jeremy ducks back home for emergency medical treatment, the gateways stop working. So do all the communication links. Jeremy and his sister are on their own, Polisso is suddenly under siege, and there's only so much you can do when cannonballs are crashing through your roof... less

In a parallel-world 21st-century San Francisco where the Kaiser's Germany won World War One and went on to dominate the world, Paul Gomes and his father Lawrence are secret agents for our timeline, posing as traders from a foreign land. They run a storefront shop called Curious Notions, selling what is in our world routine consumer technology-record players, radios, cassette decks--all of which is better than anything in this world, but only by a bit... moreIn a parallel-world 21st-century San Francisco where the Kaiser's Germany won World War One and went on to dominate the world, Paul Gomes and his father Lawrence are secret agents for our timeline, posing as traders from a foreign land. They run a storefront shop called Curious Notions, selling what is in our world routine consumer technology-record players, radios, cassette decks--all of which is better than anything in this world, but only by a bit. Their real job is to obtain raw materials for our timeline. Just as importantly, they must guard the secret of Crosstime Traffic--for of the millions of parallel timelines, this is one of the few advanced enough to use that secret against us.Now, however, the German occupation police are harassing them. They want to know where they're getting their mysterious goods. Under pressure, Paul and Lawrence hint that their supplies comes from San Francisco's Chinese...setting in motion a chain of intrigues that will put the entire enterprise of Crosstime Traffic at deadly risk. less

Teenager Annette Klein and her family are secret agents of Crosstime Traffic, sending commodities of the future back to their own timeline. During an attack she is separated from her parents, taken as a slave, and then the really scary thing happens--her purchasers take her to an unofficial crosstime portal.

Time travel doesn't work. You can't go backward or forward; you're stuck at "now". What you can do is travel sideways, to the same "now" in another timeline where history turned out differently.So far, only our home timeline has figured out how to do that. We use Crosstime Traffic to conduct discreet trading operations in less advanced timelines, selling goods just a little bit better than the locals can make... moreTime travel doesn't work. You can't go backward or forward; you're stuck at "now". What you can do is travel sideways, to the same "now" in another timeline where history turned out differently.So far, only our home timeline has figured out how to do that. We use Crosstime Traffic to conduct discreet trading operations in less advanced timelines, selling goods just a little bit better than the locals can make. It's profitable, but families who work as Time Traders have to be careful to fit in, lest the locals become suspicious. Justin's family are Time Traders. The summer before he's due to start college, he goes with them to a different Virginia, in a timeline where the American states never became a single country, and American history has consisted of a series of small wars. Despite his unease, he accompanies Randolph Brooks, another Time Trader, on a visit to the tiny upland town of Elizabeth, Virginia. He'll only be away from his parents for a few days. Beckie Royer thanks her stars that she's from California, the most prosperous and advanced country in North America. But just now she's in Virginia with her grandmother, who wants to revisit the tiny mountain town where she grew up. The only interesting thing there is a boy named Justin--and he'll be gone soon. Then war between Virginia and Ohio breaks out anew. Ohio sets a tailored virus loose on Virginia. Virginia swiftly imposes a quarantine, trapping Becky and Justin and Randolph Brooks in Elizabeth. Even Crosstime Traffic can't help. All the three of them can do is watch as plague and violence take over the town. It's nothing new in history, not in this timeline or any other. It's part of the human condition. And just now, this part of the human condition sucks. less

The Soviet Union won the Cold War. The Russians were a little smarter than they were in our own world, and the United States was a little dumber and a lot less resolute. Now, more than a century later, the world's gone Communist, and capitalism is a bad word. For Gianfranco and his friend Annarita, a couple of teenagers growing up in Milan, life in a heavily regimented, surveillance-rich command economy is just plain dreary... moreThe Soviet Union won the Cold War. The Russians were a little smarter than they were in our own world, and the United States was a little dumber and a lot less resolute. Now, more than a century later, the world's gone Communist, and capitalism is a bad word. For Gianfranco and his friend Annarita, a couple of teenagers growing up in Milan, life in a heavily regimented, surveillance-rich command economy is just plain dreary. The eventual withering-away of the state doesn't look like it's going to happen anytime soon. Annarita's a hard-working student and a member of the Young Socialists' League. Gianfranco is a lot less motivated--but on the other hand, his father's a Party apparatchik. The biggest excitement in their lives is a wargame shop called The Gladiator, which runs tournaments, and stocks marvelous complex games you can't find anywhere else. Then, abruptly, the shop is shut down. Someone's figured out that The Gladiator's games are teaching counterrevolutionary capitalist principles. The Security Police are searching high and low for the shop's proprietors, who've not only vanished into thin air, but have left behind sets of fingerprints that aren't in the records of any government on earth. Only one staffer is left: Gianfranco and Annarita's friend Eduardo. He's on the run, and he comes to them in secret with an astonishing story: he's a time trader from our own timeline, accidentally left behind when the store was evacuated. The only way Eduardo can get home to his own timeline is if Gianfranco and Annarita can help him reach one of the other time trader sites in this world--and the Security Police will be on their tails all the way there. less

Usually Crosstime Traffic concerns itself with trade. Our world owns the secret of travel between parallel continuums, and we mean to use it to trade for much-needed resources with the worlds next door. Preferably without letting them know about any of that parallel-worlds stuff.But there’s one parallel world that’s different. In it, the atomic war broke out in 1967, at the height of the Summer of Love... moreUsually Crosstime Traffic concerns itself with trade. Our world owns the secret of travel between parallel continuums, and we mean to use it to trade for much-needed resources with the worlds next door. Preferably without letting them know about any of that parallel-worlds stuff.But there’s one parallel world that’s different. In it, the atomic war broke out in 1967, at the height of the Summer of Love. Now, Crosstime Traffic has been given a different sort of mission: find out what on earth, or on the many earths, went wrong. less